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13 nm high-efficiency nickel-germanium soft x-ray zone plates
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
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2011 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 29, no 1, 011012- p.Article in journal (Refereed) Published
Abstract [en]

Zone plates are used as objectives for high-resolution x-ray microscopy. Both high resolution and high diffraction efficiency are crucial parameters for the performance of the lens. In this article, the authors demonstrate the fabrication of high-resolution soft x-ray zone plates with improved diffraction efficiency by combining a nanofabrication process for high resolution with a process for high diffraction efficiency. High-resolution Ni zone plates are fabricated by applying cold development of electron-beam-patterned ZEP 7000 in a trilayer-resist process combined with Ni-electroplating. High-diffraction-efficiency Ni-Ge zone plates are realized by fabricating the Ni zone plate on a Ge film and then using the finished zone plate as etch mask for anisotropic CHF3 reactive ion etching into the underlying Ge, resulting in a Ni-Ge zone plate with improved aspect ratio and zone plate efficiency. Ni-Ge zone plates with 13 nm outermost zone width composed of 35 nm Ni on top of 45 nm Ge were fabricated. For comparable Ni and Ni-Ge zone plates with an outermost zone width of 15 nm, the diffraction efficiency was measured to be 2.4% and 4.3%, respectively, i.e., an enhancement of a factor of 2.

Place, publisher, year, edition, pages
2011. Vol. 29, no 1, 011012- p.
Keyword [en]
Crucial parameters, Etch mask, Ge films, High efficiency, High resolution, Nanofabrication process, Resist process, Soft X-ray, Trilayers, X ray microscopy, Zone plates, Aspect ratio, Diffraction efficiency, Fabrication, Germanium, Optical instruments, Reactive ion etching, X ray diffraction, X rays
National Category
Other Engineering and Technologies
Identifiers
URN: urn:nbn:se:kth:diva-31321DOI: 10.1116/1.3520457ISI: 000286679400015Scopus ID: 2-s2.0-79551627215OAI: oai:DiVA.org:kth-31321DiVA: diva2:404728
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110318Available from: 2011-03-18 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
In thesis
1. High-Resolution Nanostructuring for Soft X-Ray Zone-Plate Optics
Open this publication in new window or tab >>High-Resolution Nanostructuring for Soft X-Ray Zone-Plate Optics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diffractive zone-plate lenses are widely used as optics in high-resolution x-ray microscopes. The achievable resolution in such microscopes is presently not limited by the x-ray wavelength but by limitations in zone-plate nanofabrication. Thus, for the advance of high-resolution x-ray microscopy, progress in zone-plate nanofabrication methods are needed.

 

This Thesis describes the development of new nanofabrication processes for improved x-ray zone-plate optics. Cold development of the electron-beam resist ZEP7000 is applied to improve the resolution of soft x-ray Ni zone plates. The influence of developer temperature on resist contrast, resolution, and pattern quality is investigated. With an optimized process, Ni zone plates with outermost zone widths down to 13 nm are demonstrated. To enhance the diffraction efficiency of Ni zone plates, the concept of Ni-Ge zone plates is introduced. The applicability of Ni-Ge zone plates is first demonstrated in a proof-of-principle experiment, and then extended to cold-developed Ni zone plates with outermost zone widths down to 13 nm. For 15-nm Ni-Ge zone plates a diffraction efficiency of 4.3% at a wavelength of 2.88 nm is achieved, which is about twice the efficiency of state-of-the-art 15-nm Ni zone plates. To further increase both resolution and diffraction efficiency of soft x-ray zone plates, a novel fabrication process for W zone plates is developed. High resolution is provided by salty development of the inorganic electron-beam resist HSQ, and cryogenic RIE in a SF6 plasma is investigated for high-aspect-ratio W structuring. We demonstrate W zone plates with 12-nm outermost zone width and a W height of 90 nm, resulting in a 30% increase in theoretical diffraction efficiency compared to 13-nm efficiency-enhanced Ni-Ge zone plates. In addition to soft x-ray zone plates, some lenses for hard x-ray free-electron-laser applications were also fabricated during this Thesis work. Fabrication processes for the materials W, diamond, and Pt were developed. We demonstrate Pt and W-diamond zone plates with 100-nm outermost zone width and respective diffraction efficiencies of 8.2% and 14.5% at a photon energy of 8 keV.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xii, 70 p.
Series
Trita-FYS, ISSN 0280-316X ; 2011:55
Keyword
zone plates; x-ray optics; x-ray microscopy; high resolution; nanofabrication; electron beam lithography; reactive ion etching; tungsten; nickel; germanium
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-47409 (URN)978-91-7501-175-2 (ISBN)
Public defence
2011-12-02, FA31, Roslagstullsbacken 21, KTH/Albanova, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111114Available from: 2011-11-14 Created: 2011-11-08 Last updated: 2011-11-14Bibliographically approved

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Hertz, Hans M.Holmberg, Anders

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